Hollow Fiber Membrane Module, Hollow Fiber Membrane Module Unit, Membrane Filtration Device Using the Same, and Method of Operating the Same

ABSTRACT

A hollow fiber membrane module using a sheet-form hollow fiber membrane having excellent cleaning properties in which the pressure resistance of a hollow fiber membrane anchor section does not deteriorate, even when the membrane area increases; a hollow fiber membrane module unit using the module; a membrane filtration device using the unit; and an operation method therefor are provided. The hollow fiber membrane module comprises sheet-form hollow fiber membranes and an anchoring member which anchors the sheet-form hollow fiber membranes in a roughly parallel manner while maintaining in an open state at least one end portion of the sheet-form hollow fiber membranes. The shape of an end face of a side of the anchoring member from which the hollow fiber membranes are exposed is roughly rectangular, and the shape of an end face of a side of the anchoring member toward which the hollow fiber membranes open is roughly circular.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of a PCT Application No.PCT/JP2003/12335, filed Sep. 26, 2003, whose priority is claimed onJapanese Patent Application No. 2002-283715, filed Sep. 27, 2002. Thecontent of both the PCT Application and the Japanese Application isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hollow fiber membrane module, ahollow fiber membrane module unit, a membrane filtration device(membrane filtration system) used for the purification of potable watersupply, purification of waste water, industrial processes or the like,and to a method of operating the same.

2. Description of Related Art

Filtration of water by means of a membrane module has been employed invarious applications due to its high separation performance, compactconstruction of the device and large-quantity and continuous processingcapability.

There are different types of membrane modules such as microfiltrationmodules, ultrafiltration modules, and reverse osmosis modules, which areselected and operated in accordance with the material to be separated.For example, the microfiltration module can efficiently remove fineparticles and microorganisms measuring 10 μm or smaller, particularly 1μm or smaller, and is therefore commonly used in the purification ofpotable water supplies and waste water.

The microfiltration module is used in the form of a hollow fibermembrane module in which hollow fiber membranes are disposed in acylindrical configuration or screen configuration, a pleated membranemodule in which a flat membrane is folded in pleats in a cylindricalconfiguration or a planar membrane module in which a flat membrane isdisposed in a screen configuration, in order to increase the membranearea and to make it easier to handle.

Among these, the hollow fiber membrane module allows it to provide alarge membrane area per unit volume and is preferably used.

Use of the hollow fiber-based microfiltration membrane module infiltration enables it to remove suspended solids and bacteria or thelike from water by means of micropores of the membrane and to produceclear filtered water. After a long period of continuous filteringoperation, however, the micropores become clogged, resulting in adecrease in flow rate of the filtered water and an increase in thefiltration pressure, thus making it necessary to frequently change themembrane module which is economically disadvantageous.

In order to prevent the membrane module from becoming clogged quickly bythe membrane clogging matter contained in water, operations to restorethe filtering function are carried out periodically such as, in the caseof an external pressure-driven hollow fiber membrane module, forexample, backwashing wherein filtered water is passed in a reversedirection from the inside to the outside of the hollow fiber membrane,scrubbing cleaning wherein the membrane is vibrated while supplying airto the outside of the hollow fiber membrane, or a combination of thesecleaning operations is carried out, thereby removing themembrane-clogging matter deposited on the outside of the hollow fibermembrane.

While the membrane area of the hollow fiber membrane module can beincreased by increasing the number of hollow fiber membranes per unitvolume, increasing the membrane area by disposing the hollow fibermembranes bundled in cylindrical configuration makes it difficult toflow the scrubbing air or backwash water for cleaning, resulting indecreasing effect of cleaning. This problem can be avoided by disposingthe hollow fiber membranes with equal spacing from each other in theform of sheets, which enables uniform cleaning of the membrane surfaceand makes it applicable also to the filtration of heavily contaminatedwater.

The hollow fiber membrane module is also used in large-scalepurification plants having processing capacity over 10,000 m³/d, in thecase of potable water purification. In such an application, a largenumber of hollow fiber membrane modules are used to secure a largemembrane area. For example, when arranging the hollow fiber membranemodules to form a unit, how close the hollow fiber membrane modules canbe arranged to each other is restricted by the sizes and configurationsof the anchoring members and the water collection section provided atthe ends of the hollow fiber membrane modules.

There has been proposed such a hollow fiber membrane module thatsatisfies the relationship 100≧A/B≧1.2, where it is assumed that thehollow fiber membranes are anchored while being left open at one end orboth ends thereof by anchoring members provided in a housing, the areaof a surface of the anchoring member is A on the side where the hollowfiber membrane is exposed from the anchoring member, and the area of anend face of the anchoring member is B on the side where the hollow fibermembrane opens (refer to Japanese Unexamined Patent Publication, FirstPublication No. H07-178320).

This module is assembled by anchoring sheet-form hollow fiber membraneswith anchoring members that are molded in elongated rectangular shape.Since width of the anchoring member on the side where the hollow fibermembrane is exposed is larger than the outer diameter of the watercollecting tube and larger than the joint, and the water collectingtubes and other members do not interfere with each other, the modulescan be disposed in parallel arrangement so that side faces of theanchoring members make contact with each other. As a result, theentirety of the hollow fiber membranes can be cleaned evenly byscrubbing without significant decrease in the density of the hollowfiber membranes.

Higher density of the hollow fiber membranes and lower processing costper unit area of the hollow fiber membrane can be achieved when thenumber of the sheet-form hollow fiber membranes fastened onto oneanchoring member is larger. However, the number of the hollow fibermembranes that can be fastened onto one anchoring member that is formedin elongated rectangular shape is limited. On the other hand, there is aproblem in that increasing the width of the rectangular anchoring memberfor the purpose of increasing the number of the hollow fiber membranesthat can be fastened causes the withstand pressure to drasticallydecrease.

There is also known a hollow fiber membrane module that has aconstitution of a plurality of sheet-form hollow fiber membranesarranged and fastened by an anchoring member onto the end of acylindrical housing, so that a proper spacing is secured between thesheet-form hollow fiber membranes so as to be efficiently cleaned whileincreasing the density of the hollow fiber membranes (for example, referto Japanese Unexamined Patent Publication, First Publication No.2000-51670).

In this module, however, since the sheet-form hollow fiber membranes arearranged in the cylindrical housing, the width of the sheet-form hollowfiber membrane fastened at the end becomes smaller than that at thecenter of the cylinder resulting in lower density of the hollow fibermembranes.

There is also known a hollow fiber membrane module having a constitutionof a bundle of hollow fiber membranes divided into a plurality ofsegments and are expanded and fastened onto a support body at a positionnear the center between potting sections on both ends, thereby improvingthe efficiency of cleaning (for example, refer to Japanese UnexaminedPatent Publication, First Publication No. H06-99038).

In this module, however, since the hollow fiber membranes are expandedand fastened onto the support body near the center between pottingsections on both ends, density of the hollow fiber membranes becomeslower and it becomes difficult to clean the portion near the pottingsections.

When the hollow fiber membrane modules are used in a large-scalepurification plant, a large number of hollow fiber membrane modules areinstalled in a submerging water tank in order to increase the membranearea. The hollow fiber membrane modules are disposed in a configurationmade up of multiple columns and multiple rows in order to make efficientuse of the space in the submerging water tank.

However, this constitution requires a large space for piping andservicing, resulting in a dead space that cannot be efficiently used. Asa result, unnecessarily large quantity of washing water is dischargedduring periodic cleaning operations, thus resulting in lower ratio ofrecovering of water.

The present invention has been made to solve the problems describedabove and an object thereof is to provide a hollow fiber membrane modulecomprising sheet-form hollow fiber membranes that can be easily cleaned,wherein withstand pressure of the hollow fiber membrane anchoringsection does not decrease even when the membrane area is increased, anda hollow fiber membrane module unit having high density of hollow fibermembranes. Another object of the present invention is to provide amembrane filtration device that employs the hollow fiber membrane moduleunit described above and a method of operating the same.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a hollow fiber membranemodule comprising: a plurality of sheet-form hollow fiber membranes (1);and an anchoring member (2) that fastens the plurality of sheet-formhollow fiber membranes (1) substantially parallel to each other whileleaving at least one end of the sheet-form hollow fiber membranes (1)open, wherein an end face of the anchoring member (2) on a side wherethe hollow fiber membranes are exposed is substantially rectangular, andan end face of the anchoring member (2) on a side where the hollow fibermembranes open is substantially circular.

In the hollow fiber membrane module according to the first aspect of thepresent invention, since the end face of the anchoring member (2) on theside where the hollow fiber membranes are exposed is substantiallyrectangular, and the end face of the anchoring member (2) on the sidewhere the hollow fiber membranes open is substantially circular,withstand pressure of the hollow fiber membrane anchoring section doesnot decrease even when the membrane area is increased in the module thatemploys the sheet-form hollow fiber membranes which can be cleanedefficiently.

It is preferable that the anchoring member (2) comprise a rectangularparallelepiped section (3) of substantially rectangular parallelepipedshape on the side where the hollow fiber membranes are exposed, and acylindrical section (4) of substantially cylindrical shape on the sidewhere the hollow fiber membranes open, since such a configurationimproves all of withstand pressure, efficiency of cleaning, and densityof the hollow fiber membranes.

It is more preferable that the relationship 0.2≦L/D≦1.0 be satisfiedwhere D (mm) is a diameter of the cylindrical section (4) and L (mm) isa length of the cylindrical section (4).

Furthermore, it is more preferable that the relationship 1.0≦W/D≦2.0 besatisfied where W (mm) is a length of the longer side of an end face ofthe rectangular parallelepiped section (3) where the hollow fibermembranes are exposed and D (mm) is a diameter of the cylindricalsection (4).

A second aspect of the present invention is a hollow fiber membranemodule unit comprising a plurality of hollow fiber membrane modules,wherein a plate-like member (5) having a hole through which thecylindrical section (4) passes is provided on a side of the sheet-formhollow fiber membranes (1) perpendicular to sheet surfaces, so that thehollow fiber membrane modules are secured in place by the plate-likemember (5).

In the hollow fiber membrane module unit according to the second aspectof the present invention, since the plate-like member (5) having thehole through which the cylindrical section (4) passes is provided, andthe hollow fiber membrane modules are secured in place by the plate-likemember (5), anchoring is achieved easily and reliably, and a highdensity of the hollow fiber membranes can be achieved.

It is preferable that the cylindrical section (4) and a water collectingcap (6) that engages with the cylindrical section (4) sandwich andfasten the plate-like member (5), so that anchoring is achieved easilyand reliably.

It is preferable that the cylindrical section (4) and the watercollecting cap (6) be fastened to each other by screw engagement sincethis allows easy dismantling.

Furthermore, it is preferable that a plurality of hollow fiber membranemodule units be stacked in the vertical direction, the sheet surface ofthe sheet-form hollow fiber membranes (1) be disposed in the verticaldirection, and water collecting caps (6) that adjoin each other in thevertical direction be connected to each other by a water collectingmember (7) that extends in the vertical direction, and a side frame (21)be disposed on a side face parallel to the sheet surfaces of thesheet-form hollow fiber membranes (1), since this configuration allowsit to increase the density of the hollow fiber membranes with a smallerinstallation area.

With this configuration, it is preferable that vertical distance betweenthe sheet-form hollow fiber membranes (1) of the hollow fiber membranemodule adjacent to each other in the vertical direction be 70 mm orless, so that the hollow fiber membranes can be cleaned efficiently.

A third aspect of the present invention is a membrane filtration devicecomprising a membrane module unit disposed in a water tank, wherein themembrane module unit comprises a plurality of hollow fiber membranemodules, each of the hollow fiber membrane modules comprises: aplurality of sheet-form hollow fiber membranes (1); and an anchoringmember (2) that fastens the plurality of sheet-form hollow fibermembranes (1) substantially parallel to each other while leaving atleast one end of the sheet-form hollow fiber membranes (1) open, and anend face of the anchoring member (2) on a side where the hollow fibermembranes are exposed is substantially rectangular, and an end face ofthe anchoring member (2) on a side where the hollow fiber membranes openis substantially circular, and the following three relationships aresatisfied where S (m²) is the membrane area of the membrane module unit,A (m²) is the area of projection of the membrane module unit, V′ (m³) isthe volume of the membrane module unit, and V (m³) is the capacity ofthe water tank:

1000≦S/A≦2000  Equation (1)

500≦S/V′≦800  Equation (2)

0.70≦V′/V≦0.99   Equation (3).

A fourth aspect of the present invention is a method of operating amembrane filtration device comprising a membrane module unit disposed ina water tank, the method comprising the steps of: forming the membranemodule unit by a plurality of hollow fiber membrane modules; forming thehollow fiber membrane modules such that a plurality of sheet-form hollowfiber membranes (1) are fastened substantially parallel to each other byan anchoring member (2) with at least one end of the sheet-form hollowfiber membranes (1) being left open, while an end face of the anchoringmember (2) on a side where the hollow fiber membranes are exposed issubstantially rectangular, and an end face of the anchoring member (2)on a side where the hollow fiber membranes open is substantiallycircular; setting S (m²), being a membrane area of the membrane moduleunit, J (m/d), being a filtration flux, T (h), being the filtrationtime, N, being the number of cycles per draining of water, D (m³), beingthe volume of draining, J′ (m/d), being the backwash flux, and T′(h),being the backwash time so as to satisfy the following relationship N≧2222.8D/{S(0.05JT−J′T′)} Equation (4); and operating the membranefiltration device.

The membrane filtration device of the present invention that has theconstitution described above and is operated by the method describedabove has a large membrane area despite having a very compactconstruction and high efficiency of cleaning, and is therefore capableof carrying out stable filtering operation over an extended period oftime.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example of a hollow fiber membranemodule of the present invention.

FIG. 2 is a sectional view of an example of anchoring member of thehollow fiber membrane module of the present invention.

FIG. 3 is a perspective view of an example of the anchoring member ofthe hollow fiber membrane module of the present invention.

FIG. 4 is a sectional view showing another example of the anchoringmember of the hollow fiber membrane module of the present invention.

FIG. 5 is a perspective view showing another example of the hollow fibermembrane module of the present invention.

FIG. 6 is a perspective view showing an example of hollow fiber membranemodule unit of the present invention.

FIG. 7 is a sectional view showing an example of the anchoring sectionof the hollow fiber membrane module unit of the present invention.

FIG. 8 is a front view showing an example of the hollow fiber membranemodule unit of the present invention stacked in the vertical direction.

FIG. 9 is diagram showing an example of a flow in membrane filtrationdevice of the present invention.

FIG. 10 is a schematic view showing an example of the bottom ofsubmerging water tank of the membrane filtration device according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in detail with reference tothe accompanying drawings.

FIG. 1 is a perspective view of an example of hollow fiber membranemodule of the. present invention.

The hollow fiber membrane module (A) is substantially constituted fromsheet-form hollow fiber membranes (1), anchoring members (2), and watercollecting caps (6). A plurality of the sheet-form hollow fibermembranes (1) are disposed in parallel to each other at equal intervalswith both ends thereof being left open and secured by the anchoringmembers (2), while the water collecting caps (6) are mounted on theanchoring members (2).

FIG. 2 shows an example of the hollow fiber membrane anchoring sectionof the hollow fiber membrane module of the present invention, in asectional view perpendicular to the direction of the sheet surface ofthe sheet-form hollow fiber membrane.

A plurality of the sheet-form hollow fiber membranes (1) are disposed inparallel to each other at equal intervals with the end thereof beingsecured by the anchoring member (2).

The end face of the anchoring member (2) on the side where thesheet-form hollow fiber membrane (1) is exposed is substantiallyrectangular and the end face of the anchoring member (2) on the sidewhere the hollow fiber membrane opens is substantially circular. In thecase in which the end face of the anchoring member (2) on the side wherethe sheet-form hollow fiber membrane (1) opens is cylindrical, farhigher withstand pressure can be achieved since deflection is smallerthan in the case of rectangular parallelepiped shape and stress isdistributed. Thus, all of the withstand pressure, efficiency ofcleaning, and density of hollow fiber membranes can be improved withthis configuration, even when a large number of sheet-form hollow fibermembranes are disposed.

In this case, the anchoring member (2) may be formed in such a shapethat changes continuously from the side where the sheet-form hollowfiber membrane (1) is exposed toward the opening end. However, thefollowing three conspicuous effects can be achieved at the same time byforming the anchoring member (2) in a constitution that has arectangular parallelepiped section (3) of substantially rectangularparallelepiped shape on the side where the hollow fiber membrane isexposed, and a cylindrical section (4) of substantially cylindricalshape on the side where the hollow fiber membrane opens, as shown inFIG. 1 and FIG. 2.

1. A large number of sheet-form hollow fiber membranes (1) can beanchored while maintaining a space from each other on the rectangularparallelepiped section (3) of one anchoring member (2), and thereforeefficient cleaning is ensured.

2. Very high density of the hollow fiber membranes can be achieved bydisposing a plurality of the hollow fiber membrane modules (A) in suchan arrangement as the side faces of adjacent rectangular parallelepipedsections (3) are in contact with each other, thereby eliminatingunnecessary space.

3. Very high withstand pressure can be achieved since the anchoringmember (2) has the cylindrical section (4) on the side thereof where thehollow fiber membrane opens.

The cylindrical section (4) of the anchoring member (2) may notnecessarily have perfectly circular cross section perpendicular to thecentral axis of the cylinder, and may be oval, modified oval, polygonalthat is approximates a circle such as a dodecagon or hexadecagon, whilea circular cross section is most preferable.

It is preferable that the relationship 0.2≦L/D≦1.0 be satisfied where D(mm) is a diameter of the cylindrical section (4) and L (mm) is a lengthof the cylindrical section in the axial direction thereof.

Withstand pressure of the hollow fiber membrane anchoring section isheavily dependent on the value of L/D of the cylindrical section (4).The value of L/D less than 0.2 leads to insufficient withstand pressure,and therefore the lower limit of L/D is 0.2 or larger, preferably 0.25or larger. The value of L/D larger than 1.0 leads to an increase in lossin an effective section of the hollow fiber membrane, and therefore anupper limit of L/D is 1.0 or less, and preferably 0.8 or less.

When the cross section of the cylindrical section (4) is not a truecircle, diameter D of the cylindrical section (4) refers to the largestsize across the cross section.

While sizes L and D of the cylindrical section (4) may be set inaccordance with the size of the hollow fiber membrane module, it becomesdifficult to install the sheet-form hollow fiber membranes (1) when D istoo small. Thus, a lower limit of D is preferably 30 mm or larger, andmore preferably 50 mm or larger. When D is too large, it is difficult toprocess the module and withstand pressure may become insufficient. Thus,an upper limit of D is 400 mm or less, and more preferably 300 mm orless.

When L is too small, a withstand pressure becomes insufficient, andtherefore a lower limit of L is preferably 10 mm or larger, and morepreferably 50 mm or larger. When L is too large, a loss in an effectivesection of the hollow fiber membrane increases and resistance to passingwater increases. Therefore an upper limit of L is 300 mm or less, morepreferably 200 mm or less.

FIG. 3 is a perspective view of an example of the hollow fiber membraneanchoring section for the hollow fiber membrane module of the presentinvention. The hollow fiber membrane module (A) of the present inventionsatisfies the relationship 1.0≦W/D≦2.0 where W (mm) is a length of thelonger side of the end face where the hollow fiber membrane is exposedand D (mm) is a diameter of the cylindrical section (4).

Increasing the value of W relative to D enables it to increase themembrane area of the hollow fiber membrane module without decreasing thewithstand pressure of the hollow fiber membrane anchoring section. Whenthe value of W/D is too large, however, the sheet-form hollow fibermembrane is drawn too tightly, thus making it difficult to arrange thesheet-form hollow fiber membranes. This results in a problem thateffective length of the hollow fiber membrane varies among thesheet-form hollow fiber membranes. Among the sheet-form hollow fibermembranes stacked one on another, those located outside have a problemthat the longer portion of the hollow fiber membrane is embedded in therectangular parallelepiped section (3), thus resulting in increasingresistance against passing water. Therefore, an upper limit of W/D is2.0 or less, and is preferably 1.8 or less.

When the value of W/D is too small, the withstand pressure decreases,although it becomes easier to process. Therefore, a lower limit of W/Dis 1.0 or larger and preferably 1.2 or larger.

While the value of W may be set in accordance with the membrane area ofthe hollow fiber membrane module, it becomes difficult to ensuresufficiently large membrane area of the module when W is too small.Therefore, a lower limit of W is at least 40 mm, and preferably at least80 mm.

When the value W is too large, it becomes difficult to process themodule. Therefore, an upper limit of W is 500 mm or less, and ispreferably 400 mm or less.

In FIG. 3, the size W is shown as the height in the case in which therectangular parallelepiped section (3) is larger in height than inwidth. In the case in which width (dimension in the direction where thesheet-form hollow fiber membranes are stacked) is larger than height, Wrepresents the width.

The length of the rectangular parallelepiped section (3) in the axialdirection of the fiber of the hollow fiber membrane may be setappropriately since the configuration of arrangement of the hollow fibermembranes varies depending on the effective length and outer diameter ofthe hollow fiber membrane, width of the sheet-form hollow fiber membraneand other factors. When the length of the rectangular parallelepipedsection (3) in the axial direction of the fiber of the hollow fibermembrane is too small; however, it becomes difficult to converge theplurality of sheet-form hollow fiber membranes having rectangularparallelepiped shapes that are disposed at equal intervals intocylindrical shape. Therefore, a lower limit for the length of therectangular parallelepiped section (3) in the axial direction of fiberof the hollow fiber membrane is preferably 5 mm or larger, and morepreferably 10 mm or larger.

When the length of the rectangular parallelepiped section (3) in theaxial direction of the fiber of the hollow fiber membrane is too large,a loss in the effective section of the hollow fiber membrane increasesand portions that do not contribute to the filtration increase resultingin increasing resistance against passing water. Therefore, an upperlimit for the length of the rectangular parallelepiped section (3) inthe axial direction of the fiber of the hollow fiber membrane is 100 mmor less, preferably 70 mm or less and more preferably 50 mm or less.

In order to collect the filtrate discharged from the hollow fibermembrane, the water collecting cap (6) is provided on the cylindricalsection (4). The water collecting cap (6) is preferably installed bybringing threads (8) formed on the circumference of the cylindricalsection (4) and threads (8) formed in the water collecting cap (6) intomesh with each other while sealing by means of a sealing member (9) suchas an O-ring, as this allows easy dismantling and reliable sealing.

FIG. 4 shows another example of the hollow fiber membrane anchoringmember of the hollow fiber membrane module of the present invention, ina sectional view along a direction perpendicular to a sheet surface ofthe sheet-form hollow fiber membrane.

In this example, the sheet-form hollow fiber membrane (1) is fastened bythe anchoring member (2) in the housing (10).

In the case in which the housing (10) is provided as in the exampleshown in FIG. 4, too, dimensions (D), (L), and (W) are determined withreference to the size of the anchoring member (2), similarly to the casewithout the housing (10).

In the case in which the housing (10) is provided, too, the watercollecting cap (6) may be installed by bringing the threads (8) formedon the circumference of the cylindrical section (4) and the threads (8)formed in the water collecting cap (6) into mesh with each other whilesealing by means of the sealing member (9) such as an O-ring. The watercollecting cap (6) may also be integrated with the housing (10).Alternatively, the water collecting cap (6) may be bonded onto theanchoring member (2).

The hollow fiber membrane module of the present invention preferablyemploys such a constitution as both ends of the sheet-form hollow fibermembrane (1) are fastened by separate anchoring members (2). When thehollow fiber membrane module is used in such a manner as raw water issupplied from the outside of the hollow fiber membrane and treated wateris taken out from the inside of the hollow fiber membrane, there is aproblem that resistance against passing water within the hollow fibermembrane increases as the effective length of the hollow fibers becomeslonger. With such a structure as shown in FIG. 1 where water iscollected from both ends of the hollow fiber membrane, resistanceagainst passing water can be decreased and the effective length of thehollow fibers can be increased. When the hollow fiber membrane modulesare assembled into a unit, it becomes easier to support by securing bothends with the anchoring members (2).

FIG. 5 is a perspective view showing another example of the hollow fibermembrane module of the present invention. The hollow fiber membranemodule (A) of this example roughly comprises the sheet-form hollow fibermembranes (1), the anchoring member (2), the water collecting cap (6),and supporting member (11). The sheet-form hollow fiber membranes (1)are disposed in parallel at equal spacing from each other on theanchoring member (2), and are secured by the anchoring member (2) at oneend thereof and are supported by the supporting member (11) at the otherend. The water collecting cap (6) is mounted on the anchoring member(2).

There are no restrictions on the structure and other features of thesupporting member (11), as long as it can support the sheet-form hollowfiber membranes (1) in parallel at equal spacing from each other. Forexample, the entire structure may be consolidated by applying a resin,or the hollow fiber membranes may be secured by means of a member thathas rod-like or thread-like shape. Furthermore, the hollow fibermembranes may be bent at the center in a U-shape, and secured at thebend by the supporting member (11).

Such a constitution wherein water is collected only on one end can beapplied to a case where effective length of the hollow fiber membrane issmall or the hollow fiber membrane has a large diameter.

When a large quantity of water is to be treated, it is preferable toassemble a plurality of hollow fiber membrane modules into a hollowfiber membrane module unit which is easier to handle. In this case, itis preferable to construct the hollow fiber membrane module unit withthe density of the hollow fiber membranes as high as possible withoutcompromising the ease of cleaning.

FIG. 6 is a perspective view showing an example of the hollow fibermembrane module unit of the present invention.

The hollow fiber membrane module unit (B) roughly comprises hollow fibermembrane modules (A), plate-like members (5), water collecting caps (6)and side frames (21).

The plate-like member (5) has four holes formed therein. With thecylindrical section (4) inserted into this hole so that the sheetsurface of the hollow fiber membrane module (A) is disposed in thevertical direction and the axial direction of the fiber of the hollowfiber membranes agrees with the horizontal direction, while the watercollecting cap (6) is attached to the protruding cylindrical section(4), the hollow fiber membrane module (A) can be fastened by theplate-like member (5).

The water collecting cap (6) can be attached easily and reliably bymeans of screw engagement between threads (8) formed on the cylindricalsection (4) and on the water collecting cap (6), as describedpreviously. In this case, as shown in FIG. 7, the water collecting cap(6) and the plate-like member (5) can be used to position and fasten thehollow fiber membrane module (A) in place by making the water collectingcap (6) larger than the hole formed in the plate-like member (5).

Four hollow fiber membrane modules (A) are fastened onto the plate-likemember (5), and the side frames (21) are attached on both sides of thesheet-form hollow fiber membrane (1) along the sheet surface, therebyassembling the hollow fiber membrane module unit (B).

While the hollow fiber membrane module unit (B) of the example shown inFIG. 6 consists of four hollow fiber membrane modules (A), the numbermay be adjusted as required.

The side frame (21) has a function to maintain the shape of the hollowfiber membrane module unit (B) and a function to concentrate the hollowfiber membranes without allowing the scrubbing air to leak to theoutside.

The side frame (21) may be a plate that has sufficient rigidity andstrength made of stainless steel or the like, but it is more preferableto use a frame made of stainless steel or the like having plates made ofresin or light alloy, which makes the structure light in weight whilemaintaining strength. It is more preferable to use transparent resinplates so that the hollow fiber membrane modules can be seen from theoutside, thus making it possible to check if the modules kept clean.

The hollow fiber membrane modules (A) are assembled into a unit withoutclearance from each other so as to make contact with each other on therectangular parallelepiped sections (3) of the anchoring member (2),thus making it possible to supply scrubbing air uniformly throughout theunit.

The hollow fiber membrane module units (B) assembled as described abovecan be arranged in plurality in the vertical direction or horizontaldirection and integrated, so that the area of the hollow fiber membranescan be readily adjusted in accordance with the processing capacity.

In this case, it is preferable to stack a plurality of the hollow fibermembrane module units (B) in the vertical direction as shown in FIG. 8to integrate the units in order to increase the density of the hollowfiber membranes per unit area, although there is a limitation by thedepth of the submerging water tank in which the hollow fiber membranemodule units (B) are disposed. The hollow fiber membrane module units(B) are stacked in, for example, 2 to 10 levels. In the case in whichthe hollow fiber membrane module units (B) are immersed incoagulation-sedimentation basin of a purification plant, the stackinglevel is preferably from 4 to 6.

Assembly of the hollow fiber membrane module units stacked in thevertical direction may also be disposed in plurality in the submergingwater tank as required.

When plural hollow fiber membrane module units (B) are stacked in thevertical direction, if vertical spacing between the sheet-form hollowfiber membranes (1) of adjacent hollow fiber membrane modules is toolarge, streams of scrubbing air tend to converge and form a thickstream, after hitting the membrane surface of the hollow fiber membranemodule located below and while rising over the membrane surface of thehollow fiber membrane module located above. This leads to weaker effectof diffusion, and uniform effect of cleaning the membrane surface cannotbe ensured for hollow fiber membrane module located at a higherposition.

For this reason, vertical spacing between the sheet-form hollow fibermembranes (1) is set to 70 mm or less, preferably 60 mm or less. Withthis construction, after hitting the membrane surface of the hollowfiber membrane module located at a low position, the scrubbing air risesto the membrane surface of the hollow fiber membrane module locatedabove while maintaining diffusion. As a result, cleaning performance isnot compromised even when the plurality of hollow fiber membrane modulesare stacked in the vertical direction.

The vertical spacing between the sheet-form hollow fiber membranes (1)herein refers to the distance between the bottom end of the anchoringsection of the sheet-form hollow fiber membrane (1) of the hollow fibermembrane module located above and the top end of the anchoring sectionof the sheet-form hollow fiber membrane (1) of the hollow fiber membranemodule located just below, and does not mean the distance between theportions that move during vibration movement of air scrubbing.

A lower limit of the vertical spacing between the sheet-form hollowfiber membranes (1) is preferably 20 mm or larger, and more preferably30 mm or larger, since the hollow fiber membranes may be entangled tomake it difficult to clean when the distance is too small.

When a plurality of hollow fiber membrane module units (B) are stackedin the vertical direction, it is necessary to collect the filtrate fromdifferent water collecting caps (6) and discharge it. It is preferableto connect the water collecting caps (6) with each other by means of thewater collecting members (7) that extend in the vertical direction, foreasy connection in compact construction.

For the water collecting members (7), union joint, flange joint,T-joint, flexible hose, coupling or the like may be used to connect thewater collecting cap (6) and the water collecting members (7), orbetween a plurality of the water collecting members (7).

The water collecting members (7) may be made of any material that hassufficient mechanical strength and durability, such as polycarbonateresin, polysulfone resin, acrylic resin, ABS resin, modified PPE(polyphenylene ether), vinyl chloride resin, polyolefin resin(polypropylene, polyethylene, etc.) and metals such as stainless steel,bronze, brass, and cast steel.

The anchoring member (2) used in the hollow fiber membrane module of thepresent invention may be made of a material that has sufficient bondingstrength with the hollow fiber membrane and the housing (10) andsatisfies the requirements of the application, including thermosettingresins such as polyurethane resin, epoxy resin, silicon resin orunsaturated polyester resin and thermoplastic resins such aspolyurethane resin, ethylene-vinyl acetate copolymer or polyolefinresin. The hollow fiber membrane may be anchored by known methods suchas pouring a thermoplastic resin that is melted by heating or applying athermosetting resin by means of centrifugal force or gravity.

When the housing (10) is used, it may be made of a material thatsatisfies the requirements of the application such as polyolefine,polycarbonate, modified polyphenylene oxide, ABS and polyvinyl chloride.A material that bonds with the anchoring member (2) with insufficientstrength may be used after applying priming treatment.

There are no restrictions on the kind of material, pore size, voidratio, membrane thickness, outer diameter, and other properties of thehollow fiber membrane used in the hollow fiber membrane module of thepresent invention. For example, the hollow fiber membrane may be made ofpolyolefin, polysulfone, polyvinyl alcohol, cellulose,polyacrylonitrile, polyamide, polyimide, polytetrafluoroethylene,polyvinylidene fluoride, or the like.

When the hollow fiber membranes are woven in order to process them toform a sheet-like structure, a material that has high elongationproperty is preferably used such as polyethylene or polypropylene sinceit is easy to perform processing.

When the hollow fiber membrane made of hydrophobic material is used inthe filtration of water, the hollow fiber membrane may be applied tomake it hydrophilic.

The hollow fiber membrane may have, for example, a pore size in a rangefrom 0.001 to 3 μm, a void ratio from 20 to 95%, a membrane thicknessfrom 5 to 500 μm, and an outer diameter from 20 to 3000 μm.

The hollow fiber membrane module (A) of the present invention comprisesa plurality of the sheet-form hollow fiber membranes (1) disposed inparallel to each other at equal intervals. While there is no restrictionon the method of arranging the hollow fiber membranes in the sheetconfiguration, a hollow fiber membrane sheet woven into sheetconfiguration is preferably used. Spacing between the sheet-form hollowfiber membranes may be set in a range, for example, from 2 to 100 mm,depending on the properties of the raw water. The number of thesheet-form hollow fiber membranes may also be set in accordance with themembrane area of the module.

FIG. 9 is a diagram showing an example of a flow in the membranefiltration device of the present invention. The membrane filtrationdevice consists substantially of a water tank (12), a hollow fibermembrane module unit (13), an air diffusing device (14), a suction pump(15), a chemical pump (16), a chemical tank (17), a backwash pump (18),a backwash tank (19), and a blower (20).

The membrane filtration device of the present invention satisfies thefollowing three relationships where S (m²) is the membrane area of themembrane module units, A (m²) is the area of projection of the membranemodule units, that is the area of the membrane module units as viewedfrom above, V′ (m³) is the volume of the membrane module units and V(m³) is the capacity of the water tank.

1000≦S/A≦2000  (1)

500≦S/V′≦800  (2)

0.70≦V′/V≦0.99  (3)

The volume V′ is the volume enclosed by the outer surface of themembrane module unit including empty space within the membrane moduleunit where no members are present.

The method of operating a membrane filtration device according to thepresent invention will now be described. The hollow fiber membranemodule unit (13) is installed in the water tank (12). The hollow fibermembrane module unit (13) has the air diffusing device (14) provided atthe bottom thereof. Filtrate is produced by running the suction pump(15), with a part of the filtrate stored in the backwash tank (19).After a predetermined period of filtration, scrubbing cleaning isperformed using air supplied by the blower (20) that is connected to theair diffusing device (14), and backwashing is carried out by thebackwash pump (18) using the filtrate that is supplied from the backwashtank (19). At this time, a chemical supplied from the chemical tank (17)is injected by the chemical pump (16) into the backwash water. Thebackwash water is discharged to the outside of the submerging water tankthrough an effluent port (not shown) provided at the top of thesubmerging water tank. Cleaning by scrubbing and backwashing may becarried out separately.

After cleaning, the liquid in the water tank (12) is drained from thebottom thereof. Draining of water may not necessarily be carried outevery time cleaning is performed, but may be carried out once aftercleaning several times. Hereinafter, the number of cleaning operationsbefore draining of water will be referred to as the number N of cyclesper draining of water. The cleaning operation herein refers to thecleaning carried out after stopping filtration and before starting thenext run of filtration.

One cleaning operation will be counted either when scrubbing cleaningand backwashing are carried out simultaneously, or when scrubbingcleaning and backwashing are carried out separately. Even when aplurality of cleaning processes are repeated in such a sequence asscrubbing cleaning, backwashing, scrubbing cleaning then backwashing,this series of cleaning processes will be counted as one cleaningoperation as long as these processes are carried out after stoppingfiltration and before starting the next run of filtration.

The cleaning may be performed either by scrubbing cleaning orbackwashing only. In a sequence of operation cycles, cleaning may beperformed either by carrying out only scrubbing cleaning or backwashing,or by combining scrubbing cleaning and backwashing. For example, themembrane filtration device may be operated in a sequence of (i)filtration, (ii) scrubbing cleaning, (iii) filtration, (iv) backwashing,and (v) draining of water, in which case the number of cycles perdraining of water is 2.

In another example, the membrane filtration device may be operated in asequence of (i) filtration, (ii) scrubbing cleaning, (iii) filtration,(iv) scrubbing cleaning, (v) backwashing, (vi) filtration, (vii)scrubbing cleaning and backwashing combined, and (viii) draining ofwater, in which case the number of cycles per draining of water is 3.

FIG. 10 is a schematic diagram showing an example of water tank bottomin the membrane filtration device of the present invention, where thesolid line shows the outline of the inside of the water tank at thebottom, and the dashed line shows the outline of the outer diameter ofthe hollow fiber membrane module unit.

Areal efficiency and volumetric efficiency of the membrane module unitswill now be described. Areal efficiency is given by dividing themembrane area S of the membrane module units by the projection area A ofthe membrane module units (the area a′(m)×b′(m) in the example shown inFIG. 10). Volumetric efficiency is given by dividing the membrane area Sof the membrane module units by the volume V′ (m³) of the unit (thevolume a′(m)×b′(m)×height of unit (m: not shown) in the example shown inFIG. 10).

Capacity V (m³) of the submerging water tank is given by a (m)×b(m)×effective depth of water (m: not shown) in the example shown in FIG.10.

In the membrane filtration device of the present invention, arealefficiency S/A of the hollow fiber membrane module unit is preferably ina range from 1000 to (m²/m²) and more preferably in a range from 1100 to(m²/m²). While areal efficiency can be adjusted by changing the numberof units stacked, the unit cannot be made compact when the unit isconstituted by stacking a small number of levels and areal efficiency islower than (m²/m²). When the unit is constituted by stacking a largenumber of levels and areal efficiency is higher than 2000 (m²/m²), forexample in the case in which the air diffusing device is installed onlyat the bottom of the unit, on the other hand, bubbles may not bedistributed throughout the membrane located high in the unit, thusresulting in insufficient cleaning.

In the membrane filtration device of the present invention, volumetricefficiency S/V′ of the membrane module units is preferably in a rangefrom 500 to 800 (m²/m³) and more preferably in a range from 600 to 700(m²/m³). When volumetric efficiency S/V′ is lower than 500 (m²/m³), thedevice becomes larger. When volumetric efficiency S/V′ is higher than800 (m²/m³), efficiency of cleaning decreases.

In the membrane filtration device of the present invention, capacity V(m³) of the submerging water tank and volume V′ (m³) of the membranemodule unit preferably satisfy the relationship 0.70≦V′/V≦0.99. When theratio V′/V is lower than 0.70, dead space becomes larger, whichdecreases the water recovery ratio. When the ratio V′/V is higher than0.99, on the other hand, clearance between the submerging water tank andthe unit installed in the submerging water tank becomes smaller, thusgiving rise to the possibility of breaking the unit when installing it.

According to the method of operating a filtration device of the presentinvention, membrane area S (m²) of the membrane module unit, filtrationflux J (m/d) that is the quantity of filtered water (m³/D) divided bythe membrane area S (m²), filtration time T (h), the number of cyclesper draining of water N, quantity of drained water per one cycle D (m³),backwash flux J′ (m/d) that is the quantity of backwash water (m³/D)divided by the membrane area S (m²) and backwash time T′ (h) satisfy thefollowing relationship.

N≧22.8D/{S(0.05JT−J′T′)}

Water recovering ratio Q (%) is given by the following equation.

$\begin{matrix}{Q = {\left\{ \frac{\left( {{{Quantity}\mspace{14mu} {of}\mspace{14mu} {filtered}\mspace{14mu} {water}} - {{Quantity}\mspace{14mu} {of}\mspace{14mu} {backwash}\mspace{14mu} {water}}} \right)}{\left( {{Quantity}\mspace{14mu} {of}\mspace{14mu} {raw}\mspace{14mu} {water}\mspace{14mu} {supply}} \right)} \right\} \times}} \\{100} \\{= \left\{ {\left( {{S \times J \times {T/24} \times N} - {S \times J^{\prime} \times {T^{\prime}/24} \times N}} \right) \times} \right.} \\{\left. \left( {{S \times J \times {T/24} \times N} + D} \right) \right\} \times 100}\end{matrix}$

While the water recovering ratio Q (%) is dependent on various factors,it is affected particularly heavily by the number N of cycles perdraining of water. When it is assumed that water recovering ratio Q(%)≧95, the relationship described above that defines N becomes asfollows.

N≧22.8D/{S(0.05JT−J′T′)}

In a purification plant having a large capacity, quantity of drainage islarge and the water recovering ratio becomes more important. Therefore,the value of the number of cycles per draining of water N is determinedby the relationship described above, so as to achieve a high waterrecovering ratio of 95% or higher.

While the filtration flux J (m/d) can be determined in consideration ofthe raw water quality, it is preferably in a range from 0.25 to 2.5 m/d.When filtration flux is less than 0.25 m/d, filtration must be continuedfor a very long period of time and, when filtration flux is more than2.5 m/d, suction pressure may become high at an early stage.

While filtration time T (h) can be determined in consideration of theraw water quality, it is preferably, for example, in a range from 15 to240 minutes, more preferably from 30 to 120 minutes. When the filtrationtime is shorter than 15 minutes, water recovering ratio and rate ofoperation become low. When filtration time is longer than 180 minutes,cleaning restoration performance of the suction pressure may becomelower.

While the quantity of scrubbing air, that is, the quantity of air perunit projection area of the membrane module units may also be determinedappropriately, it is preferably, for example, in a range from 100 to 400(Nm³/(m²·h)), more preferably in a range from 150 to 250 (Nm³/(m²·h)).When the quantity of air is less than 100 (Nm³/(m²·h)), effect ofcleaning decreases. When the quantity of air is more than 400(Nm³/(m²·h)), there is a tendency that supply of excessively largequantity of air is required.

While the scrubbing cleaning time may also be determined appropriately,it is preferably, for example, in a range from 1 to 10 minutes, morepreferably from 2 to 5 minutes. When the scrubbing cleaning time is lessthan 1 minute, cleaning effect becomes insufficient. When the scrubbingtime is longer than 10 minutes, rate of operation becomes low.

While backwash flux J′ (m/d) may also be determined appropriately, it ispreferably, for example, in a range from 0.3 to 4 times the filtrationflux, more preferably in a range from 1 to 3 times the filtration flux.When backwash flux is less than 0.3 times the filtration flux, cleaningeffect becomes insufficient. When backwash flux is longer than 4 timesthe filtration flux, water recovering ratio becomes low.

While the backwash time T′ (h) may also be determined appropriately, itis preferably, for example, in a range from 5 to 180 seconds, morepreferably from 10 to 90 seconds. When the backwash time is less than 5seconds, cleaning effect becomes insufficient. When the backwash time islonger than 90 seconds, water recovering ratio and rate of operationbecome low.

While chemical injected during backwashing may be selected as required,for example, sodium hypochlorite aqueous solution may be used.Concentration of the injected chemical may also be determinedappropriately, but it is preferably, for example, in a range from 1 to100 mg/L (concentration in backwash water), more preferably in a rangefrom 2 to 50 mg/L. Chemicals may not necessarily be injected, or may beinjected as required.

The number of cycles per draining of water N may be set to one for everybackwashing, or one for several backwash operations. Preferably,drainage is performed, for example, once per every one to four backwashoperations, more preferably once per every one or two backwashoperations. When drainage is performed less than once per four backwashoperations, suction pressure may increase prematurely.

TEST EXAMPLES

The present invention will now be described in more detail below by wayof Test Examples.

Production of Hollow Fiber Membrane Module Test Example 1

A hollow fiber membrane made from porous hydrophilic polyethylene(product name EX540T, inner diameter 350 μm, outer diameter 540 μm, madeof polyethylene manufactured by Mitsubishi Rayon Co., Ltd.) was used tomake the sheet-form hollow fiber membrane by folding a bundle of 16hollow fiber membranes and weaving the folded hollow fiber membraneswith stitching threads (fabric width 950 mm, number of bundled threads:70).

27 sheets of the sheet-form hollow fiber membrane were stacked at 6 mmpitch (the pitch refers to the distance between centers of thesheet-form hollow fiber membranes) by inserting fabric spacers, andinserted into a housing made of ABS resin having rectangularparallelepiped section at one end where hollow fiber membrane is exposedand cylindrical section at one end where hollow fiber membrane opens(inner diameter of cylindrical section 124 mm). Then 1.5 kg of a pottingresin C4403/N4221 (two-pack curing type polyurethane resin manufacturedby Nippon Polyurethane Industry Co., Ltd.) was injected to bond andfasten the sheet-form hollow fiber membrane onto the housing.

The sheet-form hollow fiber membrane was bonded and fastened similarlyonto the housing also on the other end. Then hollow fiber membranes werecut at both ends so as to become open, thereby producing the hollowfiber membrane module having the structure shown in FIG. 4 (membranearea 34 m², W=173 mm, D=124 mm, L=50 mm, length of hollow fiber membraneanchoring section of rectangular parallelepiped section 20 mm, L/D=0.40,W/D=1.40).

Test Example 2

The hollow fiber membrane module was produced similarly to Test Example1 except for using 1.3 kg of the potting resin (membrane area 37 m²,W=173 mm, D=124 mm, L=35 mm, length of hollow fiber membrane anchoringsection of rectangular parallelepiped section 20 mm, L/D=0.28,W/D=1.40).

Test Example 3

The hollow fiber membrane made from porous hydrophilic polyethylene(product name EX780T, inner diameter 500 μm, outer diameter 770 μm, madeof polyethylene manufactured by Mitsubishi Rayon Co., Ltd.) was used tomake sheet-form hollow fiber membrane by folding a bundle of 6 hollowfiber membranes and weaving the folded hollow fiber membranes withstitching threads (fabric width 950 mm, number of bundled threads: 82).

30 sheets of the sheet-form hollow fiber membrane were stacked at 6 mmpitch by inserting fabric spacers, and inserted into a housing made ofABS resin having rectangular parallelepiped section at one end wherehollow fiber membrane is exposed and cylindrical section at one endwhere hollow fiber membrane opens (inner diameter of cylindrical section145 mm). Then 1.7 kg of the potting resin the same as that of TestExample 1, was injected to bond and fasten the sheet-form hollow fibermembrane onto the housing. Then the hollow fiber membranes were cut atthe end so as to become open, thereby producing the hollow fibermembrane module having the structure shown in FIG. 5 (membrane area 30m², W=232 mm, D=145 mm, L=60 mm, length of hollow fiber membraneanchoring section of rectangular parallelepiped section 30 mm, L/D=0.41,W/D=1.60).

Test Example 4

The sheet-form hollow fiber membrane was produced similarly to TestExample 1, except for changing the fabric width to 1200 mm and thenumber of bundled threads to 167.

27 sheets of the sheet-form hollow fiber membrane were stacked at 12 mmpitch by inserting fabric spacers, and one end thereof was inserted intoa potting fixture made of silicon resin having rectangularparallelepiped shape on the side where the hollow fiber membrane isexposed and cylindrical shape on the side where the hollow fibermembrane opens (inner diameter 250 mm). Then 5.2 kg of the potting resinsimilar to that of Test Example 1 was injected to bond and fasten thesheet-form hollow fiber membrane.

The sheet-form hollow fiber membrane was also bonded and fastenedsimilarly on the other end. Then the hollow fiber membranes were cut atboth ends so as to become open, thereby producing the hollow fibermembrane module having the structure shown in FIG. 1 (membrane area 90m², W=425 mm, D=250 mm, L=150 mm, length of hollow fiber membraneanchoring section of rectangular parallelepiped section 50 mm, L/D=0.60,W/D=1.70).

Comparative Example 1

A hollow fiber membrane module was produced similarly to Test Example 1,except for using a housing having rectangular parallelepiped shaperanging from the end where the hollow fiber membrane is exposed to theother end where the hollow fiber membrane opens (pressure receiving areameasuring 121 mm on the longer side and 100 mm on the shorter side: sameas the pressure receiving area of the cylindrical section in TestExample 1) and applying 2.0 kg of potting resin (membrane area 35 m²,anchoring member measuring 121 mm on the longer side and 100 mm on theshorter side, with length of hollow fiber membrane anchoring section 70mm).

Repetitive Pressure Endurance test of Hollow Fiber Membrane Module

Repetitive pressure endurance test was conducted on the hollow fibermembrane module made in Test Examples 1 to 4 and Comparative Example 1.

Test samples for the repetitive pressure endurance test were made bycutting off the hollow fiber membrane from the hollow fiber membranemodule and sealing the open end of the hollow fiber membrane with thepotting resin. The test samples were set on a repetitive pressureendurance test device, and were subjected to a repetition of applicationand removal of pressure on the end of the module, to determine thenumber of pressure cycles before leakage occurred in the sample(temperature 40° C., pressure 350 kPa, ON for 30 seconds and OFF for 30seconds per cycle, pressure applied on the end of module, number ofcycles 5000 at maximum). Test results are shown in Table 1.

TABLE 1 Test Test Test Test Comparative Example 1 Example 2 Example 3Example 4 Example 1 No. of 5000 5000 5000 5000 1530 cycles (No leak) (Noleak) (No leak) (No leak) (Crack in potting surface)

It is clear from the results of the repetitive pressure endurance testthat the hollow fiber membrane module of the present invention has ahigh withstand pressure.

Production of Hollow Fiber Membrane Module Unit Test Example 5

A hollow fiber membrane module unit (membrane area 136 m²) having astructure shown in FIG. 6 was made by using the hollow fiber membranemodule made in Test Example 1. Furthermore, the hollow fiber membranemodule unit having a structure shown in FIG. 8 with an air diffusingdevice provided at the bottom was made by stacking the hollow fibermembrane module units in 6 levels in the vertical direction (membranearea 816 m², a′=1.2 m, b′=0.4 m, unit height 2.637 m, areal efficiencyS/A=1700 m²/m², unit volume V′=1.266 m³, volumetric efficiency S/V′=645m²/m³).

Test Example 6

A hollow fiber membrane module unit was made similarly to that for TestExample 5 except for stacking hollow fiber membrane module units in fourlevels in the vertical direction (membrane area 544 m², a′=1.2 m, b′=0.4m, unit height 1.797 m, areal efficiency S/A=1133 m²/m², V′=0.863 m³,volumetric efficiency S/V′=630 m²/m³).

Filtration Test Test Example 7

The hollow fiber membrane module unit made in Test Example 5 wasinstalled in the membrane filtration device shown in FIG. 9 (a=1.21 m,b=0.41 m, effective water depth 2.637 m, V=1.31 m³, V′/V=0.97).

The membrane filtration device described above was subjected tounderflow water filtration test for 10 days, to observe the change inthe suction pressure. Test conditions are shown in Table 2 and theresults are shown in Table 3.

Test Example 8

The underflow water filtration test was conducted similarly to TestExample 7 except for setting the tank to a=1.3 m, b=0.5 m, effectivewater depth to 2.637 m, V=1.71 m³ and V′/V=0.74. Test conditions areshown in Table 2 and the results are shown in Table 3.

Test Example 9

The hollow fiber membrane module unit made in Test Example 6 wasinstalled in the membrane filtration device shown in FIG. 9 (a=1.21 m,b=0.41 m, effective water depth 1.797 m, V′/V=0.97). The membranefiltration device described above was subjected to underflow waterfiltration test for 10 days, to observe the change in the suctionpressure. Test conditions are shown in Table 2 and the results are shownin Table 3.

Test Example 10

The underflow water filtration test was conducted similarly to TestExample 9 except for setting the tank to a=1.3 m, b=0.5 m, effectivewater depth to 1.797 m, V=1.17 m³ and V′/V=0.74. Test conditions areshown in Table 2 and the results are shown in Table 3.

Comparative Example 2

The underflow water filtration test was conducted similarly to TestExample 7 except for setting the tank to a=1.5 m, b=0.7 m, effectivewater depth to 2.637 m, V=2.77 m³ and V′/V=0.46. Test conditions areshown in Table 2 and the results are shown in Table 3.

Comparative Example 3

The underflow water filtration test was conducted similarly to TestExample 9 except for setting the tank to a 1.5 m, b=0.7 m, effectivewater depth to 1.797 m, V=1.89 m³ and V′/V=0.46. Test conditions areshown in Table 2 and the results are shown in Table 3.

TABLE 2 Comparative Test Examples Examples 7 8 9 10 2 3 Areal efficiency(m²/m²) 1,700 1,133 1,700 1,133 Volumetric efficiency (m²/m³) 645 630645 630 V/V′ 0.97 0.74 0.97 0.74 0.46 0.46 Filtration J (m/d) 2.0 0.52.0 0.5 T (h) 1 1 Cleaning Scrubbing Air flow rate 200 (Nm³/(m²/h))Duration (h) 2 Back- J′ (m/d) 4.0 1.0 4.0 1.0 washing T′ (h) 0.00833Draining D (m³) 1.07 0.47 0.731 1.01 2.53 1.73 Number of cycles per 1 12 3 1 4 draining of water N

TABLE 3 Comparative Test Examples Examples 7 8 9 10 2 3 Suction pressureimmediately 28.0 28.0 15.0 15.0 28.0 15.0 after starting test_(20° C.)(kPa) Suction pressure after end of 30.0 29.7 15.5 15.4 29.6 15.3test_(20° C.) (kPa) Water recovering ratio (%) 96.8 96.3 95.3 95.5 94.894.7

The results of the filtration test show that the membrane filtrationdevice of the present invention achieves a water recovery ratio as highas 95% or higher while maintaining stable suction pressure duringoperation.

The hollow fiber membrane module, the hollow fiber membrane module unit,the membrane filtration device and the method of operating the sameaccording to the present invention are used for purification of apotable water supply, purification of waste water, industrial processesor the like. In the hollow fiber membrane module of the presentinvention, since the end face of the anchoring member (2) on the sidewhere the hollow fiber membrane is exposed is substantially rectangular,and the end face of the anchoring member (2) on the side where thehollow fiber membrane opens is substantially circular, withstandpressure of the hollow fiber membrane anchoring section does notdecrease even when the membrane area is increased in a module thatemploys the sheet-form hollow fiber membrane having high efficiency ofcleaning. In the hollow fiber membrane module unit of the presentinvention, since the plate-like member (5) that has a hole through whichthe cylindrical section (4) passes is provided so that the hollow fibermembrane modules are secured in place by the plate-like member (5), easyand reliable anchoring is ensured while improving the density of thehollow fiber membranes. The membrane filtration device of the presentinvention that includes a plurality of the hollow fiber membrane modulesof the present invention and is operated by the operation method of thepresent invention has a large membrane area in spite of very compactconstruction and allows efficient cleaning, and therefore stablefiltration can be continued over a long period of time.

1-11. (canceled)
 12. A method of operating a membrane filtration devicecomprising a membrane module unit disposed in a water tank, the methodcomprising the steps of: forming the membrane module unit by a pluralityof hollow fiber membrane modules; forming the hollow fiber membranemodules such that a plurality of sheet-form hollow fiber membranes arefastened substantially parallel to each other by an anchoring memberwith at least one end of the sheet-form hollow fiber membranes beingleft open, the anchoring member having a first side and an opposingsecond side, a first end face that is substantially rectangular on saidfirst side where outer surfaces of the hollow fiber membranes areexposed at said first end face, and a second end face that issubstantially circular on said second side of said anchoring memberwhere the at least one end of the hollow fiber membranes left open is atsaid second face; setting S (m²), being a membrane area of the membranemodule unit, J (m/d), being a filtration flux, T (h), being a filtrationtime, N, being the number of cycles per draining of water, D (m³), beingthe volume of draining, J′ (m/d), being the backwash flux, and T′(h),being the backwash time so as to satisfy the following relationshipN≧22.8D/{S(0.05JT−J′T′)}  Equation (4); and operating the membranefiltration device.